1. Field of the Invention
The invention pertains to a piston-cylinder unit with a protective sleeve which can be fitted over a mounting unit on the end of the piston rod.
2. Description of the Related Art
A piston-cylinder unit in the form of a gas spring, for example, or a vibration damper, consists primarily of a cylinder with an end part and a piston rod with a piston at one end and a mounting element at the other end, as well as a piston rod guide between the two ends, which, when the two main components are assembled, are pushed into the cylinder and rolled, beaded, or screwed in the area of the piston rod guide
The piston rod assembly also includes a protective sleeve, which is intended to protect the piston rod against mechanical damage. The protective sleeve is often so long, that, when the piston rod is in its maximum outward-travel position, there is a slight overlap between the protective sleeve and the cylinder. As a result, it may not be possible to roll or bead the cylinder in the area of the piston rod guide. Another difficulty is that the cylinder cannot be painted until after the assembly process is complete. In DE 1 995 281 U and in DE 1 951 754 U, a support disk is attached to the piston rod, and the protective sleeve is attached to the disk. In the design according to DE 1 995 281 U, the protective sleeve can be pushed over the mounting element afterwards. This protective sleeve has no end part. The protective sleeve according to DE 1 951 754 U does not have an end part either. So that the protective sleeve can be aligned with the cylinder with sufficient precision in spite of this, the support disk is provided with a guide sleeve, but this sleeve must again be of sufficient length.
U.S. Pat. No. 4,167,991 also discloses a protective sleeve for a vibration damper. This sleeve is made of flat strip material and is mounted radially on a profiled retaining disk, after which the two edges are butt-welded together.
U.S. Pat. No. 6,474,216 pertains to a vibration damper with a protective sleeve, which can also be attached to support disk at the end of the assembly process. A radially split connecting ring, which has a guide bushing for the protective sleeve, can be pushed onto the support disk of the piston rod. The guide bushing has a circumferential groove, into which the protective sleeve can be pushed from the direction of the cylinder to secure the connecting ring in place. This design principle can be applied to conventional vibration dampers or gas springs, but it is often not possible to apply it to spring struts with wheel or axle mounts, because the radial dimension of the mounts is larger than the inside diameter of the protective sleeve, and thus the tube cannot be pushed over the cylinder toward the support disk.